Chemical vapor infiltration and chemical vapor deposition (CVI/CVD) are well-known processes for forming composite materials. In particular, CVI/CVD is a useful process for fabricating structural composites such as brake disks, combustors and turbine components.
In general, the term “chemical vapor infiltration” (CVI) implies deposition of a matrix within the pores of a substrate, and “chemical vapor deposition” (CVD) implies deposition of a surface coating on a substrate. However, as used herein, the term CVI/CVD is intended to refer generally to infiltration and deposition of a matrix on and within a substrate.
CVI/CVD generally includes passing a gas (e.g., methane, propane, etc.) comprising a reactant component (e.g., carbon) around and through a substrate. The reactant component deposits on and within the pores of the substrate to form a composite structure. When the substrate and reactant component both comprise carbon, for example, a carbon/carbon composite material is formed.
In some conventional CVI/CVD processes, several substrates are stacked within a process chamber (i.e., a furnace) in order to increase the number composite structures produced per batch. During treatment, the process conditions (i.e., temperature, pressure and flow rate of the gas) within the chamber are controlled and/or varied to create the desired thermal and pressure gradients and to facilitate the deposition of the matrix within the substrate.
However, there are several disadvantages associated with such conventional systems and methods for performing CVI/CVD. For example, using conventional CVI/CVD processes, the temperature and pressure gradients are likely to vary at different locations within the process chamber causing the rate and amount of deposition of the matrix to vary from substrate to substrate, dependent upon the location of the substrate within the process chamber.
Moreover, the exhaust systems of such conventional CVI/CVD process systems tend to be less efficient and require more power to operate, often resulting in the undesirable formation of soot on the substrates as well as build-up of carbon residue within the process chamber, typically requiring shut down of the system for cleaning and maintenance.
As such, improved systems and methods for performing CVI/CVD that increase uniformity of the composite structures and efficacy of the CVI/CVD process are desired.